1. Field of the Invention
The present invention relates to a data transfer system for transferring data from a data transmission apparatus to a data reception apparatus via a parallel interface, and a data transfer system for printer, which uses this data transfer system.
2. Description of the Related Art
A host computer, such as a personal computer, prepares data and sends it to a printer. The printer edits the received data from the host computer and print it out.
A data transfer system, which comprises a host computer and a printer, controls data exchange between the host computer and printer using an interface apparatus.
Interface apparatuses used in such a system typically use a Centronics compatible parallel interface.
In sending data to a printer from a host computer using a Centronics compatible parallel interface, the host computer sets data (DATA) byte by byte on a data line of its own interface, as shown in FIG. 15.
When the DATA is set, the host computer then changes a signal Strobe on a control signal line to a low level from a high level.
When detecting this level change, the printer sets a signal Busy on another control signal line to a high level and receives the DATA from the host computer.
When data reception is complete, the printer sets an signal nAck on another control signal line to a low level.
When the signal Busy on its control signal line is at a high level, the host computer stops sending data to the printer. When detecting that the signal nack on its control signal line becomes a low level, the host computer confirms that the printer has received the data, and prepares for transmission of the next data to the printer.
Popular printers for use in a system, which comprises a host computer and a printer, receive a vast amount of data from the host computer and print the data, such as a monochrome laser printer and a color laser printer.
Such printers are demanded to print a variety of data from mainly characters to characters mixed with graphics or image data, and the amount of data the printers handle tends to ever increases.
Laser printers, different from ordinary wire or thermal dot printers, employ an electronic photographic system in their print mechanisms, so that printing, once started, cannot be controlled to be temporarily stopped.
To use a low-speed interface to send data from a host computer to a printer, therefore, the printer is provided with a memory with a one-page capacity, called a page memory, so that the printer stores all the received data from the host computer into this page memory and then activates the print mechanism to print that data.
To print data of A4 size at 300 dpi, for example, the page memory needs a capacity of about 1 megabytes.
Conventional Centronics compatible parallel interfaces are a low-speed type that takes time in data transmission, thus requiring that printers be provided with a large-capacity page memory. This will inevitably increase the cost.
When an ink-jet printer or a thermal printer which uses a line head system to ensure fast printing is used as a printer, a Centronics compatible parallel interface, if used, takes time in data transmission, preventing the printer from sufficiently demonstrating its fast-printing performance.